With reference to FIG. 1, a fuel cell 10 is an electrochemical device that uses chemical reactions to produce useful electricity directly, rather than through a stepwise conversion of chemical energy to mechanical energy or heat. Fuel cells are thus not bound by the Carnot efficiency limits for heat engines and can be significantly more efficient than technologies such as internal combustion.
The core of the fuel cell 10 includes a membrane-electrode assembly (MEA) 12, comprising an anode 14, electrolyte membrane 16, and cathode 18, forming a sandwich-like configuration. In a proton-conducting hydrogen-air fuel cell, hydrogen oxidation occurs at the anode 14, producing protons and electrons. The electrolyte membrane 16 is conductive only for protons, and so the electrons produced flow through an external load, doing useful work. At the cathode 18, oxygen is reduced and activated oxygen reacts with protons to form water. In the case of devices operating at temperatures above 100° C., the water produced is gaseous rather than liquid.